The specifications of the Advanced Configuration and Power Interface (ACPI) define six operating states (power states) from S0 state to S5 state. In S0 state, a computer operates, and a processor (CPU) and other devices can automatically transition to a power-saving mode for operation based on the algorithms set thereto in accordance with the access frequency and the load status. S1 state to S4 state are called sleeping states, where the CPU stops execution of instructions.
The ratio of reduction in power consumption increases in the order from S1 to state to S4 state, and a time required for resumption of S0 state from each state increases in this order. S3 state is called suspend or standby where the context of the processor in S0 state is stored in a main memory and electric power to the main memory is secured. S4 state is called hibernation where the context of the processor and the content stored in the main memory are stored in a nonvolatile recording medium. S5 state is a soft-off state where the power consumption is the same as in S4 state.
A notebook personal computer (hereinafter called a laptop PC) may use an operating mode of lid-close-no action. In this operating mode, when a Liquid Crystal Display (LCD) case that holds the LCD is closed, an operation of the LCD only is stopped and a system maintains S0 state. The lid-close-no action is suitable for an operating mode such that a laptop PC is not used for a short time, because the PC can resume S0 state in a short time.
Japanese Patent Application Publication No. 2005-352897 teaches a technique of avoiding malfunction during transfer of a laptop PC. The embodiment of this document defines a transfer mode as a new operating mode so as to ensure safety against dropping of the PC during transfer for a short time such as transfer between an office and a meeting room, while shortening a resumption time. According to this document, when a lid is closed so as to place the laptop PC into the transfer mode, the operation of a CPU is continued, reading/writing requests to a hard disk drive (HDD) are stored in a queue and a head of the HDD is withdrawn from the above of the disk.
Meanwhile, a laptop PC may include an application program (hereinafter called an application) for chatting installed therein enabling real time conversation using a wireless network. Such a chat application is equipped with a function to display a login status of the person on the other end of conversation on a screen, and once a session configured is disconnected during transfer of the laptop PC, his/her log-out state will be shown on a screen on the other end. In this case, although he/she is not able to make a response only for a short time due to transfer, the person on the other end will misjudge due to the disconnection of the session that he/she is not able to respond for a long time, thus impairing prompt information exchange. In order to maintain a session of the chat application even during transfer, electric power has to be supplied to devices such as a CPU, a main memory and a wireless module, and related programs have to be in an executable state.
On the other hand, since a user does not conduct any job with the laptop PC during transfer, power consumption thereof is desirably minimized. From S1 state to S4 state of the ACPI, since a CPU does not execute an instruction, a wireless network cannot be maintained or a session of the chat application cannot be maintained. In S3 state, since it may take a long time to resume, such a state does not offer sufficient convenience as a temporary power-saving mode.
In order to maintain specific functions such as a chat application and a wireless network, an operating system (OS) also has to be kept in an executable state. However, an OS such as WINDOWS® includes a task scheduler incorporated therein to automatically execute an application, so that a large number of processes may be executed at a predetermined reserved time. Thus, while maintaining specific functions, the automatic operation of such processes increases the utilization of a processor or drives a device consuming a lot of power such as a HDD. Therefore sufficient reduction in power consumption cannot be achieved. Further, applications include an antiviral program that issues warning when the execution of corresponding processes is stopped, and therefore it is difficult for another program to forcibly stop such an application. Additionally, since such an antiviral program frequently accesses a HDD, sufficient power-saving cannot be achieved unless the access is stopped.
In the transfer mode of the embodiment in Japanese Patent Application Publication No. 2005-352897, network connection can be maintained even when a laptop PC is not used for a short time due to transfer and a resumption time of a normal mode is shorter than in S3 state. In addition, an access operation to a HDD is suspended, so that power consumption of the HDD can be reduced. However, since programs that do not access the HDD continues to operate as usual, the utilization of the CPU increases with the operation of these programs. The CPU consumes the maximum power among devices of a computer. Therefore, it cannot be said that the transfer mode in Japanese Patent Application Publication No. 2005-352897 is sufficient from the viewpoint of reduction in power consumption of a laptop PC during transfer. Similarly it cannot be said that the operating mode of lid-close-no action is sufficient, because power consumption thereof is large during transfer. Therefore, another operating mode has been demanded, which is capable of maintaining specific functions such as a chat application and a wireless network and being free from an increase in power consumption due to functions that need not be maintained.